The present invention relates to a semiconductor manufacturing apparatus and more particularly to the semiconductor manufacturing apparatus such as an ion implanter which implants an ion beam on a semiconductor and treats the semiconductor wafer at a low temperature.
The most popular semiconductor manufacturing apparatus is an ion implanter in which, as shown in FIG. 2, ions emitted from an ion source 1 forms an ion beam 4 and are deflected in a elbow duct 5 so as to be separated according to mass thereof by an electric magnet 3. The respective ions having a predetermined mass are selected by a slit 6 so as to be implanted into the semiconductor wafer 7 in an implanting room 8. The semiconductor wafer installed on a wafer 7 holder of the ion implanter is cooled using cooling water so as to decrease a thermal resistance between the wafer and the wafer holder and to effectively cool the semiconductor wafer.
Examples of an ion implanter are found in, for example; Japanese Patent Laid-open No. 63-133442 (1988) and 64-42577 (1989) and U.S. Pat. Nos. 4,458,746, 4,537,244 and 4,806,769.
But in the conventional semiconductor manufacturing apparatus which use water as a coolant for the wafer holder, the temperature of the semiconductor wafer becomes rather high because of the high thermal resistance between the wafer and the wafer holder.
Recently, it has become necessary to cool the semiconductor wafer below water freezing temperature 0.degree. C. in order to effectively treat the wafer. Some conventional semiconductor manufacturing apparatus uses liquid Nitrogen as refrigerant,; however, since the temperature of liquid Nitrogen is very cold, the pipe or connecting part of the pipe for the liquid Nitrogen either becomes frozen or frosted from moisture in the air. Such freezing or frosting is serious problem for the semiconductor manufacturing apparatus. Furthermore, it is difficult for the conventional semiconductor manufacturing apparatus to control the temperature of the wafer holder with high accuracy because of its very low temperature and wide temperature control range such as from a room temperature to -200.degree. C.